The present invention relates to processing of granulated blast-furnace slag, and in particular to a method and a system for preventing granulated blast-furnace slag from solidifying due to its latent hydraulic property.
Granulated blast-furnace slag is a very useful material since it can be used as blast-furnace cement or as a substitute for sand used as fine aggregate for construction work.
Granulated blast-furnace slag has a glass-like three-dimensional net structure. The spaces in this structure are irregularly filled with calcium ions. Therefore, granulated blast-furnace slag including moisture solidifies over time when subjected to a simple external stimulus, such as an alkaline stimulus. This means that granulated blast-furnace slag has a latent hydraulic property.
The latent hydraulic property is a property whereby calcium ions that come into contact with water become calcium hydroxide (Ca(OH)2) having a fluidity and particles of granulated blast-furnace slag combine with each other to become a big mass through the agency of this calcium hydroxide.
Once granulated blast-furnace slag solidifies, the solidified granulated blast-furnace slag becomes a very hard solid mass. Therefore, a large amount of effort is required to break the solidified granulated blast-furnace slag into pieces for use as blast-furnace cement. Also, the blast-furnace cement formed using such pieces will not solidify to a regular hardness.
It should be noted here that the granulated blast-furnace slag is formed by bringing molten slag whose temperature is extremely high, such as 1200xc2x0 C. into contact with water to rapidly cool the molten slag. Therefore, molten slag is necessarily brought into contact with water to form granulated blast-furnace slag. As a result, calcium hydroxide (Ca(OH)2) is inevitably produced.
Needless to say, even if calcium hydroxide (Ca(OH)2) is produced, the solidification of granulated blast-furnace slag will still take a certain amount of time. However, granulated blast-furnace slag is used as a material for blast-furnace cement on a massive scale. Therefore, it is preferable that granulated blast-furnace slag stays in a stable state without solidifying for a long time.
Various methods have been proposed to prevent granulated blast-furnace slag from solidifying due to its latent hydraulic property. For instance, Japanese Laid-Open Patent Application No. 54-131504 discloses a method of preventing the solidification by maintaining the pH of cooling circulation water used for manufacturing granulated slag at 6.5 or less. Also, Japanese Laid-Open Patent Application Nos. 54-127895, 54-131504, and 54-112304 disclose methods of preventing the solidification by bringing granulated blast-furnace slag into contact with carbon dioxide gas during or after a coarsely crushing process.
In the former method, an acid is added to the blast-furnace slag to cause a neutralization reaction between the acid and the calcium ions in the slag. As a result, the solidification property is weakened. In the case of the method using carbon dioxide, the same neutralization reaction occurs. It should be noted here that in the case of the method using carbon dioxide, carbon dioxide does not directly react to calcium ions but is absorbed into the moisture existing on the surface of the granulated blast-furnace slag or in the air and a small amount of carbonated water is generated. The small amount of carbonated water reacts with the calcium ions, causing a neutralization. As a result, the increase in pH is inhibited and the granulated blast-furnace slag is prevented from solidifying.
With the conventional method where the pH of the cooling circulation water is maintained at 6.5 or less, however, an acid, such as hydrochloric acid, sulfuric acid, or phosphoric acid, needs to be managed. It is hazardous and difficult to manage strong acids, such as hydrochloric acid and sulfuric acid. Also, cooling circulation water is usually sprayed to granulate molten slag whose temperature is high (around 1200xc2x0 C.). Therefore, only water evaporates and acid becomes extremely concentrated around cooling units, which may lead to corrosion of the equipment.
Furthermore, with the first conventional method, the temperature of cooling circulation water becomes extremely high, as described above. Therefore, when carbonated water is used as the cooling circulation water, the carbon dioxide in the carbonated water will be aerified. As a result, the effects of the carbonated water will not be obtained.
On the other hand, the method of preventing the solidification by bringing granulated blast-furnace slag into contact with carbon dioxide gas during or after a coarsely crushing process requires a considerable processing time, even if the moisture content of granulated blast-furnace slag is increased. Therefore, this method is inappropriate to successive processing in actual factories where hundreds or thousands of tons of granulated blast-furnace slag is manufactured. Also, it is very difficult to have carbon dioxide gas evenly permeate granulated blast-furnace slag.
With regard to the above problems, the object of the present invention is to provide a safe, easy-to-manage, successive, and swift method and system for preventing the granulated blast-furnace slag from solidifying.
To solve the stated problems, the solidification prevention method for granulated blast-furnace slag of the present invention includes: a first step for generating carbonated water by dissolving carbon dioxide gas in water; and a second step for immersing granulated blast-furnace slag in the generated carbonated water after the granulated blast-furnace slag has been cooled. Here, in the first step, exhaust gas from an existing blast-furnace facility may supply the carbon dioxide gas.
To solve the stated problems, the solidification prevention system for granulated blast-furnace slag of the present invention includes: a carbonated water generation unit; and a granulated blast-furnace slag processing unit. The carbonated water generation unit includes: a reaction unit for generating carbonated water by dissolving carbon dioxide gas in water; a water inflow opening for allowing the water to flow into the reaction unit; a gas inflow opening for allowing the carbon dioxide gas to flow into the reaction unit; and a carbonated water outflow opening for allowing the generated carbonated water to flow out of the reaction unit.
The granulated blast-furnace slag processing unit includes: a storage vessel for storing the generated carbonated water; a carbonated water inflow opening for allowing the generated carbonated water to flow into the storage vessel; a slag introduction unit for introducing granulated blast-furnace slag into the storage vessel; and a slag discharge unit for discharging the granulated blast-furnace slag from the storage vessel.
The solidification prevention system may further include: a first cooling unit for cooling and granulating molten slag; a second cooling unit for cooling granulated blast-furnace slag generated by the first cooling unit; and a transport unit for transporting the granulated blast-furnace slag to the slag introduction unit immediately after the granulated blast-furnace slag has been cooled by the second cooling unit.
The solidification prevention system may further include a water circulation unit for circulating water remaining in the storage vessel for use as the water for generating the carbonated water.